OnPropertyChange event access from the ViewModel

[kcabral817]

How do I get the event in the ViewModel that a field was changed in the BO? I have a collection in the businessBase class that I need to consume and redirect to the message window of the view model. But I am unable to figure out how to monitor the OnPropertyChange event from the view model.

[rockfordlhotka]

Which ViewModel? Xaml, Blazor, etc?

[kcabral817]

xaml wpf

[rockfordlhotka]

I'm assuming CSLA 5.

There is an OnModelChanged method you can override. In your override you must invoke the base implementation or other behavior will break.

In this override you can hook and unhook the events of the Model (business domain object), including PropertyChanged. This is from memory, so might not be quite right, but something like this:

protected override void OnModelChanged(T oldValue, T newValue)
{
  if (oldValue is INotifyPropertyChanged npc)
    npc.PropertyChanged -= ModelPropertyChanged;
  if (newValue is INotifyPropertyChanged npc)
    npc.PropertyChanged += ModelPropertyChanged;
}

private void ModelPropertyChanged(object s, PropertyChangedEventArgs e)
{
  // handle the event here
}

[rockfordlhotka]

I'd put this code in a custom base class so you don't need to write/maintain it in every viewmodel class. That way it is abstracted and isn't so complicated.

The alternative is that you could submit a PR to add a ModelPropertyChanged event to ViewModelBase in CSLA 5 (the v5.x branch) and 6 (the main branch), to put this functionality into the core framework.

[kcabral817]

I would be interested in submitting a PR for both 5 & 6. I need to see how to do it, as I've done this before.

[rockfordlhotka]

That is fantastic!

Here's a doc on how to use git with CSLA. Please let me know if you have any questions, happy to help!

https://github.com/MarimerLLC/csla/blob/main/docs/dev/csla-github-flow.md

[kcabral817]

Rocky,

I'm on this step: git checkout -b 123-feature-branch marimer/

I'm going to use the v5.5.1 what should the name 123-feature-branch & be?

[rockfordlhotka]

Sorry @kcabral817 - took me a while to get time to reply 😔

git checkout -b 2672-propertychange marimer/v5.x

That'll create a new branch on your workstation named 2672-propertychange that is based off the marimer/v5.x branch, which is the maintenance branch for CSLA 5.

Anywhere in the doc where marimer/main is used, you must use marimer/v5.x, because that's the branch you are updating.